Molecular absorption of Cherenkov light at CTAO

TL;DR

This paper analyzes molecular atmospheric effects on Cherenkov light transmission at CTAO, emphasizing the importance of atmospheric monitoring to reduce uncertainties in gamma-ray observations.

Contribution

It provides a detailed analysis of molecular extinction processes and proposes an atmospheric calibration strategy for CTAO to improve measurement accuracy.

Findings

Seasonal variations affect Rayleigh scattering and molecular absorption.

Atmospheric events like stratosphere-to-troposphere transport impact Cherenkov light transmission.

Proposed calibration strategies can mitigate atmospheric uncertainties.

Abstract

The Cherenkov Telescope Array Observatory (CTAO) is the next-generation observatory for high energy \gamma-ray astronomy with unprecedented sensitivity and accuracy. Accurate estimation and mitigation of systematic uncertainties are crucial for its scientific performance. Atmospheric properties significantly influence both the generation and extinction of Cherenkov light generated by gamma and cosmic rays interacting in the atmosphere. This study provides a detailed analysis of molecular extinction processes, including Rayleigh scattering and molecular absorption, and their impact on the transmission of Cherenkov light. We examine typical summer and winter behaviour of Rayleigh scattering and seasonal and event-driven variations of the main absorbing molecules, such as ozone and nitrogen oxides, at the two CTAO array sites. Using simulations, we assess the effects of these variations on image intensity and trigger effective area, particularly during dynamic atmospheric events like stratosphere-to-troposphere transport. Based on our findings, we propose an atmospheric monitoring and calibration strategy to ensure that the CTAO meets its systematic uncertainty requirements, particularly for low-energy gamma-ray observations.